Pre-imaged high resolution hot stamp transfer foil, article and method

ABSTRACT

Pre-imaged high resolution transfer foil comprising a carrier having a surface. A releasable hardcoat is disposed on the surface. A vacuum coating is deposited on the hardcoat and an image formed in the vacuum coating.

This is a division of application Ser. No. 453,046 filed Dec. 12, 1989,U.S. Pat. No. 5,002,312 which is a continuation of 07/189,620 filed May3, 1988, abandoned.

This invention relates to a pre-imaged high resolution transfer foil,article and method and more particularly to such a pre-imaged highresolution hot stamp transfer foil, article and method which can beutilized with flexible and rigid substrates, as well as transparent andopaque substrates.

Heretofore hot stamp transfer foils have been provided in conjunctionwith hot stamp machines to stamp images on to various substrates such aspaper, plastic film and even rigid substrates. Typically the image isformed by utilizing a metal die into which the desired image has beencut. This die is placed in the hot stamping machine and is used to pressthe image into hot stamp foil utilizing a combination of heat andpressure. Typically a heat activated adhesive is placed on the back sideof the foil which upon the application of heat becomes tacky in regionsof the heated image and adheres to the paper or plastic substrate. Theresolution and image which is formed in this manner is on the order of0.1 mm at best. This is due to the fact that heat introduced during theprocess spreads out radially through the adhesive and the substrate. Ifthe hot stamping foil carrier substrate is thicker than approximately 48gauge, the image which is created has edges which are ragged, i. e., theedges are fringed because the radially spreading heat spreads furtherthan the thicker substrate. This phenomenon also occurs if the hardcoat(the release layer) and the adhesive are thick. Thus it is desirablethat the substrate as, for example, PET (polyethyleneterephthalate) theadhesive and the hardcoat must be at an optimum thickness. If the PET istoo thin it will tear in the hot stamping machine and not survive thevacuum metalizing step. If it is too thick, then the above-describedfringing results. If the hardcoat is too thin then the hot stamp foilwill not release properly or will not give the transfer image enoughscratch and mar protection. If the adhesive is too thin, it will notadhere to the substrate upon which the hot stamping image is beingplaced. If it is desired to vacuum deposit multilayer optical coatingswhere the coating itself is quite thick, the PET must be at least 142gauge and preferably 200 gauge in thickness. This thickness is requiredso that the heat load arising from the heat of condensation and from theradiant heat from the evaporating source does not deform the web onwhich the stamping is being made. Depositing materials such asdielectrics, for example, metal oxides, fluorides, sulfides and the likeare particularly prone to wrinkling the web. At the thickness of 142gauge for PET substantial fringing results in the hot stampedtransferred image. This fringe when lightly brushed causes the hotstamped image to flake at the edges of the image. At high productionspeeds this flaking results in the hot stamping machine becomingcontaminated with debris. Furthermore, the image is also subject toflaking phenomenon and is unsightly and unacceptable. There is thereforea need for a new and improved hot stamp transfer foil article and methodfor making the same.

In general, it is an object of the present invention to provide apre-imaged high resolution hot stamp transfer foil, article and method.

Another object of the invention is to provide a foil, article and methodof the above character in which the image formed is of graphic quality.

Another object of the invention is to provide a foil, article and methodof the above character in which the edges of the transferred image areencapsulated to provide an image which is environmentally resistant.

Another object of the invention is to provide a foil, article and methodof the above character in which additional levels of security can beprovided.

Another object of the invention is to provide a foil, article and methodof the above character in which an optically variable device isutilized.

Additional objects and features of the invention will appear from thefollowing description in which the preferred embodiment is set forth indetail in conjunction with the accompanying drawings.

FIG. 1 is a plan view of an article in the form of an employee badgewhich incorporates the present invention.

FIGS. 2, 3, 4, 5 and 6 are cross-sectional views showing the varioussteps in the method used for making the foil and an article of thepresent invention.

In general, the pre-imaged high resolution transfer foil consists of acarrier having a surface, a releasable hardcoat disposed on the surfaceof the carrier, a vacuum coating disposed on the hardcoat and an imageformed in the vacuum coating.

In general the article of the present invention is comprised of asubstrate having a surface. An adhesive is disposed on the surface. Avacuum coating is carried by and is secured to the adhesive. An etchedimage is formed in the vacuum coating and a protective coat is providedon the vacuum coating. If desired, an overprint can be provided on theprotective coat.

In general in the method a carrier film is provided. A releasablehardcoat is deposited on the carrier film, a vacuum coating is thendeposited on the releasable hardcoat. A photo-resist is deposited on thevacuum coating and the photo-resist is exposed to an image. Thephoto-resist is thereafter developed in a conventional etching solutionto provide a foil carrying an etched image lying solely in a plane asshown in FIG. 3. A substrate serving as a carrier film is then providedand an adhesive is provided on the image side of the foil or on thesubstrate. Heat and pressure is then utilized to transfer the image onthe foil to the substrate with the adhesive being disposed between theimage and the substrate. After the transfer has been made, the carrierfilm is removed.

More in particular, the pre-imaged high resolution transfer foil,article and method may now be described in conjunction with FIGS. 1-6.In FIG. 1, there is shown an employee badge or article 11 incorporatingthe present invention. The employee badge utilizes a substrate 12 formedof a suitable relatively rigid material such as a clear thickpolycarbonate. The card as shown is rectangular in form and is providedwith a front surface 13 on which there appears conventional printing 14,a stripe 16 indicating the security classification of the employee, adate 17 indicating the date of hire of the employee, a logo 18 of theemployer and a patterned optical variable device photograph 21 of theemployee made in accordance with the present invention as hereinafterdescribed. The employee badge 11 also is provided with a slot 22 whichcan be utilized for a strap secured to suitable fastening means such asa clip (not shown) to facilitate wearing of the badge by the employee.

In producing the image or photograph 21 which is shown on the badge 11the method which is shown in FIGS. 2-6 is utilized.

In accordance with the present invention as shown in FIG. 2, a carrierfilm 26 formed of a suitable material is provided. The carrier can be ofa relatively flexible plastic material as, for example, PET(polyethyleneterephthalate) of a suitable gauge ranging fromapproximately 40 gauge to 200 gauge. The carrier 26 is provided with asurface 27 upon which there is deposited a release hardcoat layer 28.The release hardcoat 28 can be of any suitable material such as anorganic wax, an acrylic type coating having wax components or a siliconetype release material, all well known to those skilled in the art. It ismerely necessary that the hardcoat layer have integrity during a vacuumcoating process hereinafter described and have the capability inconnection with a hot stamping process or a transfer roll-on process sothat the carrier can be released from the device it carries.

After the release hardcoat layer 28 has been deposited, a layer 29 isdeposited which can be characterized as the optical coating which is toreceive the image. Typically this optical coating can be in the form ofa single metal layer or in the form of a multilayer optical coating. Byway of example, the optical coating can be in the form of an opticallyvariable device such as disclosed in U.S. Pat. No. 4,705,356 co-pendingapplication. A layer 31 of photo-resist is then deposited over the layer29. The photo-resist can be of a conventional type, and can be either anegative or positive photo-resist. The photo-resist 31 is then exposedto the image to be incorporated into the coating 29. The image iscarried by the negative 32. In order to provide improved resolution andto replicate the grey shades in the negative, a dot screen 33 can beutilized if desired. The photo-resist is exposed through the image 32and the dot screen 33 utilizing ultraviolet light provided by anultraviolet light source 34. If desired, the dot screen 33 can beutilized for placing hidden messages or other covert features into thedesign in the coating 29.

After the photo-resist has been exposed, it can be developed by anappropriate developer depending on whether a positive or negativephoto-resist is utilized. After the photo-resist is developed to removecertain portions of the photo-resist so that the image is provided inthe photo-resist to expose the optical coating 29 therebelow. Theassembly which is shown in FIG. 2 is subjected to an etching step by asuitable etchant which can etch the optical coating 29. Typically thiscan be an acid or alkaline etch or FeCL₃ (ferric chloride) in the caseof copper etching.

The portion of the optical coating exposed through the photo-resist isthen etched away so that the image is carried into the optical coating.After the etching operation has been completed, the remainingphoto-resist can be removed in a stripping operation by a suitablephoto-resist stripper to provide the assembly shown in FIG. 3 which canbe identified as a foil lying in a single plane that carries the desiredetched image in the optical coating which is secured to the carrier 26by the release coat 28.

Let it be assumed that it is now desired to deposit the image carried bythe foil 36 into a substrate 38 of interest which is provided with asurface 39 on which it is desired to deposit the image. A coat or layerof adhesive 41 is then placed on the surface 39 of the substrate 38 oralternatively, the adhesive layer 41 can be placed over the opticalcoating 29 carrying the image. In the drawing, the adhesive is shownbeing deposited on the surface 39. After the adhesive layer 41 has beenapplied, the carrier carrying the image can then be brought into contactwith the substrate 38. Typically this is accomplished by utilizing heatand pressure utilizing a flat die stamp in a reciprocating hot stampingmachine or in a roll on transfer process using heated pressure rollers.The time and pressures required for such a step are well known to thoseskilled in the art. As soon as this transfer has been effected, thecarrier 26 can be stripped away so that there remains the article 42which is comprised of the substrate 38, the adhesive 41 which securesthe optical coating 29 to the substrate covered by the release coat 28.

The release hardcoat 28 can be left in place to protect the image. Ifdesired, an additional protective overcoat 46 can be provided. Alsoprinting 47 of a conventional type can then be printed on the overcoat46.

It has been found that in accordance with the present invention bypre-imaging the hot stamp foil 36 the thickness of the carrier can beincreased as well as the thickness of the adhesive and the hardcoatwithout adversely affecting the quality of the hot stamp image. In fact,the transferred image is of a much higher quality than can be obtainedwith conventional hot stamping processes. In addition, there are nofringes formed in the image and the image is of graphic quality. Thus itcan be seen that the present invention can be readily adapted for use onnumerous commercial hot stamp products which are presently on the marketsuch as greeting cards, paperback book covers, decals and consumeritems, packaging and the like, none of which at the present time havegraphic quality images or pictures thereon.

By utilizing the present invention it has been found that in addition toobtaining a graphic quality image that the image is also encapsulatedalong the edges by the bonding of the adhesive to the hardcoat outsideof the image area which makes the transferred image more environmentallyresistant.

When an optical variable coating is utilized for the coating 29, it ispossible to use the hot stamp image as a security device. Thetransferred image not only shifts from one color to another in reflectedlight as the viewing angle is changed but it also has a shift from apositive to a negative image in going from reflected to transmittedlight. In addition, by providing the optically variable thin filmcoating with a magnetic layer as described in co-pending applicationU.S. Pat. No. 4,838,648, issued Jun. 13, 1989, a still further securityfeature can be incorporated into the single image device which greatlyenhances the anticounterfeiting capabilities of the device. The devicealso can incorporate printing. If the printing is of a small size sothat it only could be seen under a microscope, another level of securitycould be provided to provide a total of five security features, threeovert and two covert, the photograph, color shift with viewing angle,positive to negative image reversal, magnet, property, and microscopicprinting encoded into photograph.

The present invention relates itself to many types of products ashereinbefore described. For example, the invention lends itself toplastic identification cards of the type shown in FIG. 1 and in which anOVD photograph of the person can be incorporated into the card. Anoptical variable device incorporating the present invention having thehigh resolution graphics could be used as a seal of authenticity ondocuments, or for example, on currency. By way of example, the opticalvariable device could be in the form of a photograph of the president,founder or ruler of the country for that currency. Other securitydocuments such as passports could utilize such optically variable devicephotographs.

Although the present invention has been described in conjunction withhot stamp foils, it should be appreciated that the method taught hereincan be used to apply images directly to optical coatings which arecoated directly onto the plastic film. In those situations where theoptical coating is deposited directly onto a clear carrier film only thephoto-resist coating steps (coating, exposure to UV light anddeveloping) are necessary. If a colored carrier film is used, additionalinteresting effects can be generated. For example, the color of thecarrier film can be adjusted to match one of the colors of the opticalvariable device so that at a certain angle as, for example, normalviewing, the optically variable device would not be obviously visible asit would blend into the background. At a different viewing angle,however, it would stand out against the background.

In connection with the above it should be appreciated that the substrateof interest 38 can be transparent or opaque. It can be flexible orrigid. Thus six security features can be built into a single device. Thecolor shifter in reflected light, the shift from a positive in reflectedlight to a negative image in transmitted light, the photograph itself,magnetic qualities with a magnetic layer, microprint images within theOVD and overprinting for the device.

Also it should be appreciated that the present invention can be used bypreimaging a hot stamp foil comprised of a thin layer of aluminumdeposited on a thin layer, i.e., 48 gauge PET. The 48 gauge material iscapable of withstanding the heat when the aluminum is deposited in avacuum chamber. This construction could be utilized in the embodiment ofthe invention shown in FIG. 3. The image would be formed only in thealuminum layer and the release hardcoat would be dyed with a solidcolor. This construction provides a non-shifting colored image on thesubstrate or carrier.

It is apparent from the foregoing that there has been provided apre-imaged high resolution transfer of foil, article and method whichlends itself to many applications, particularly those whereanticounterfeiting is important.

What is claimed is:
 1. In a method for producing a high resolution imageof graphic quality on a substrate, providing a carrier, depositing arelease coat on the carrier, depositing a vacuum deposited coating onthe release coat, etching an image of graphic quality in the vacuumdeposited coating to form edges with voids therebetween, placing anadhesive either on the vacuum deposited coating or on the substrate,bringing the substrate and the carrier into engagement with each otherso that the image carried by the carrier comes into engagement with theadhesive, applying heat and pressure to the carrier and the vacuumcoating carried thereby to cause the vacuum deposited coating having theetched image therein to be bonded to the adhesive whereby the edges areencapsulated and separating the carrier from the vacuum depositedcoating.
 2. A method as in claim 1 wherein the step of etching the imagein the vacuum deposited coating is accomplished by depositing aphotoresist on the vacuum deposited coating, exposing the photoresist toan image, developing the photoresist to provide a pattern of the imagein the photoresist, etching the pattern of the photoresist into thevacuum deposited coating and removing the photoresist after the etchinghas been completed.
 3. A method as in claim 1 together with the step ofapplying a protective coat on the vacuum coating.
 4. A method as inclaim 3 together with the step of applying overprinting on theprotective coat.
 5. A method as in claim 1 wherein the vacuum depositedcoating is formed by evaporating a metal.
 6. A method as in claim 1wherein the vacuum deposited coating is formed by depositing amultilayer thin film coating to form an optically variable device andwherein the etching is carried out by etching a single layer of themultilayer coating.